Lesson video

Hello, I'm Mrs. Panchal, and I'm here to do some maths learning with you today.

I can't wait to learn lots of new things and hopefully have lots of fun.

So let's get started.

Today's lesson is called Add and subtract two from odd numbers within 10, and it comes from the unit Addition and subtraction facts within 10.

By the end of this lesson, you should be able to add and subtract two from an odd number within 10.

Here are the key words for this lesson.

Odd, even, two more, and two less.

Let's have a practise.

My turn.

Odd.

Your turn.

My turn.

Even.

Your turn.

My turn.

Two more.

Your turn.

My turn.

Two less.

Your turn.

Well done.

Now that we know how to use them, let's get using them.

Here is our lesson outline for today.

The first part of the lesson, we're going to be adding two to odd numbers within 10.

And the second part of our lesson, we're going to be subtracting two from odd numbers within 10.

In this lesson, we are going to meet Sam and Jacob.

They're going to help us with our learning today.

First up, let's practise counting in just our odd numbers, because that's really going to help us with our learning today.

Can you see our first odd number on the number line that we are going to start with? 1.

That's right.

So we're gonna start with our 1, and we're gonna count through the odd numbers.

Remember, those odd numbers are all the numbers with the extra 1 at the top.

Are we ready? 1, 3, 5, 7, and 9.

Let's do that one more time.

1, 3, 5, 7, 9.

Fantastic! Now remember, we don't always have to start with the first odd number, we can start anywhere on our number line.

So let's start with the number 3.

3, 5, 7, 9.

Well done! Jacob uses his cubes to build a sequence of only the odd numbers.

He starts with 1, then he builds 3.

What number do we think he's gonna build next? Then he builds 5.

And we can see how he's building it there.

The next number will be 7.

And finally, he builds a 9 tower.

Fantastic! That looks really great, doesn't it? But Jacob then notices something when he was building his odd number sequence.

Each time, he added another group of 2.

So we can see that he had 1, he added the group of 2, which made 3.

He added a group of 2, which made 5.

Another group of 2 made 7.

And another group of 2 made 9.

Let's use that learning to find out what odd number is missing from this sequence.

I can see 1, 3, and I can see 7 and 9.

Which odd number is missing from this sequent? 5 is missing from this sequence.

Let's see how Jacob worked it out.

"I know that the missing number must be 5 because, when I added a group of 2 cubes to 3, it gave me 5." Well done, Jacob.

And well done to you if you got that correct too.

Jacob now practises counting in odd numbers using his number line.

He knows that when he was building his towers, he had to add 2 more each time to get to the next odd number.

So he's now going to use this on his number line.

He's going to start with 1, and he's going to move to 3.

He knows that he needs to add 2 more.

3 to 5, he will add 2 more.

5 to 7, how many will he add? 2 more.

And if he adds 2 more to 7, what number will he land on next? 9.

Fantastic, well done! Let's have a go at this.

So what is the missing number? I can see that in my problem I have 7, and it's asking me what is 2 more than 7? The number line is there to help you.

Is it A, 4, B, 5, or C, 9? Hmm.

So 2 more than 7.

I know if we go up in 2s, it will be the next odd number.

The next odd number is 9.

So 9 is the correct answer, because 9 is the next odd number after 7.

Well done if you got that correct too.

Now let's look at this idea as an equation and using a 10 frame.

So, 5 plus 2.

We're gonna start off by putting 5 counters onto our 10 frame, and start with a number 5 on our number line.

We're gonna add 1 more, which will give me 6.

And then, I'm going to add 1 more, which will give me 7.

We know that adding 1 more is less efficient than adding 2.

So Sam decides to just jump straight into adding 2.

She knows that 5 plus 2 will equal 7, the next odd number after 5.

So 5 plus 2 is equal to 7.

Now let's have a look at a word problem.

First, there were 7 pencils in the pot.

Then, Jacob put 2 more pencils in.

How many pencils are there? How many pencils are in there now? Let's write an equation to represent this.

We know that Jacob first had 7 pencils in the pot.

So there's our 7 pencils.

He then adds 2 more pencils.

He puts 2 more in.

So we know that we are adding 2 to that 7.

Jacob has remembered that he added 2 more pencils to an odd number.

Jacob has remembered that he has added 2 more pencils to an odd number.

So 7 plus 2 must be the next odd number.

So what do we think is the next odd number? 9.

Jacob now has 9 pencils in his pot, because 9 is the next odd number after 7.

Well done if you've got that correct.

Here is another one.

How many pets does Sam and Jacob have all together? Write an equation to match the picture and complete the bar model.

Jacob has 1 cat, Sam has 2 dogs.

Together, they have 1 cat and 2 dogs.

So Sam has said that that's 1 plus 2.

1 is a part and 2 is a part.

So how many pets do they have all together? What is the whole that we are looking for? 1 plus 2 is equal to 3.

Fantastic! When we add them together, the sum is 3.

So 3 is the whole.

2 more than 1 is the next odd number.

The odd number is 3.

Sam says that she can use this equation to now help her solve this second equation.

2 plus 1 equals? The add-ins are the same but they're in a different order.

What does that mean? How can Sam use the first one to help her solve the second one? That's correct, Sam.

Addition is commutative.

So that means we can swap the add-ins around, but the sum will remain the same.

So if 1 plus 2 is equal to 3, 2 plus 1 must also be equal to 3.

Now that's a really useful thing to remember when we are solving addition problems during today's lesson.

We can swap the addends around, but the sum will remain the same.

Jacob thinks that when 1 addend is 2, you can always think that 2 more will give the next odd number.

Sam agrees with him, because she remembers that if you change the order of the addend, the sum remains the same.

So it doesn't matter if 2 is your first addend or your second addend, the sum will still be the same.

So let's have a go.

3 plus 2.

2 more than 3 will give the next odd number.

So what is the next odd number after 3? 5.

Well done! And we can see here in this next equation that the addends have been swapped over: 2 plus 3.

It doesn't matter which order they're in, the sum will remain the same.

So what will be the answer to that equation? 5.

Well done.

5 plus 2.

The next odd number after 5? 7.

And 2 plus 5? We're swapping those addends around, but the sum will remain the same.

7.

Well done.

7 plus 2? Nine.

Well done.

So 2 plus 7 must be? 9.

Well done.

Okay, you've done such a super job with that so far, I think it's time for a task.

So what I would like you to do is to find the missing numbers to complete these equations.

Remember, adding 2 in any order gives the next odd number.

So you've got some equations to have a go at, then you've got some missing parts in some number lines and missing parts in bar models.

So pause this video, have a little go, and come on back to find out how you did.

Right, let's see how we got on.

So 3 plus 2, we can see that as the next odd number after 3, which is? 5.

7 plus 2? 9.

5 plus 2? 7.

Ooh, well, 2 plus 1.

I can see that the addends have been swapped around.

The 2 is the first addend.

But remember, it doesn't matter what order we put them in, we can still see it as it's the next odd number.

So I can see that the odd number we are looking at is 1.

The next odd number will be? 3.

Well done if you got that right.

Next up, we have our partial number lines.

I can see that the first one is starting with 5 and adding 2 more.

I can see this as the next odd number on the number line, which will be? 7.

And then the next one we can see we've got 7.

I'm adding 2 more to 7.

What's that missing number going to be? 9.

Next up, we have some bar models.

So I can see that 2 is a part and 1 is a part.

So 2 plus 1.

The next odd number after 1 is 3.

The whole must be 3.

Now this last one is a little bit tricky because I know my whole, but I only know one of the parts.

So I can see that 2 more than a number is 9.

I know that when we add 2 to an odd number, it gives the next odd number.

So 9 must be the next odd number.

What is the odd number before 9? The answer is 7.

Well done if you got that one, because that one was a little bit tricky.

Well done, some super hard work there, I'm very impressed.

So let's move on to the next part of our lesson, where we are going to be looking at subtracting 2 from odd numbers within 10.

Let's practise counting backwards in the odd numbers.

So we've already counted forwards, now we're going to count backwards.

So which odd number am I going to start with? What is our biggest odd number? That's 9.

So we're going to start with our 9, and we're gonna count backwards to the next odd number, which is 7.

The next one is 5.

The next one is 3.

And finally, 1, the smallest odd number.

Let's have another go at that.

Ready? 9, 7, 5, 3, and 1.

But remember, we can count from any number on our number line, so let's start with 5.

5, 3, 1.

Well done! Jacob now creates a backward sequence of odd numbers using his cubes.

He first builds a tower of 9.

He then builds a tower of 7.

He then builds a tower of 5.

He then builds a tower of 3.

And finally, a tower of 1.

What did you notice there? How did Jacob make his different towers? Jacob noticed that to create his backward sequence of odd numbers, he had to remove a group of 2 from the tower each time.

So to make his tower of 7, he removed a group of 2 from his tower of 9.

To build his 5, he removed a group of 2 from his tower of 7.

Sam also notices something when she's counting backwards using her number line.

"It's the same steps as when I added, but the number is decreasing." So to get to the previous odd number, we must subtract 2 each time.

So to get from 9 to 7, I will subtract 2.

To get from 7 to 5, I will subtract 2.

If I subtract 2 from 5, what number will I reach? 3.

And if I subtract 2 from 3, it will give me 1, the odd number before 3.

Let's have a go at this.

So what odd number is missing from the sequence? I can see 3, 5, 7, and 9.

The odd number missing is the odd number before 3.

2 less than 3 is 1.

So the missing number must be 1.

1 is the first odd number in the sequence.

Well done, Sam, and well done to you if you got it too.

Now it's time for you to have a turn.

What's the missing number here? 2 less than 9.

2 less than 9.

So I can see 9 on my number line.

2 less than 9 would be the previous odd number.

So what number is missing from my number line? 7.

7 is the odd number before 9.

So 2 less than 9 must be 7.

Sam notices something, though.

6 couldn't have possibly been the correct answer because she knows that you subtract 2 from an odd number and the result is odd.

And we know that 6 is an even number, so that couldn't have possibly have been the answer.

Well done if you spotted that.

Let's look at this idea now as an equation and using our 10 frame, and continuing to use our number line.

3 subtract 2.

So you can see that I've already got my 3 counters on my 10 frame.

I'm going to subtract 2.

And that will leave me with 1.

And you can see that there we have used the most efficient method.

We have used subtracting 2, rather than subtracting 1 and 1 more.

We know that it's the previous odd number, which is 1.

3 subtract 2 is equal to 1.

Over to you.

So Sam is now solving a problem using her 10 frames.

Which 10 frame would be equal to this example? First, Sam put 7 counters.

She subtracts 2.

So what would her 10 frame look like now? You might also want to use your knowledge of 2 less than 7.

Will it be A, B, or C? I can see that if I subtract 2 counters from 7, it will leave me with 5 counters.

5 is the odd number before 7.

You may have also used that knowledge to help you solve this one.

Well done! Now let's use our knowledge to complete this bar model.

Let's have a look.

What information can we see? Well done, Sam.

5 is the whole and 2 is a part.

So Sam knows that she needs to solve 5 subtract 2, or 2 less than 5.

How are we going to work out what the other part is? Sam starts on 5 and subtracts 2 using her number line, and that shows her that the missing part is 3.

3 is the odd number before 5 when I count in my odd numbers.

So 3 must be the missing part.

Sam used some different knowledge to help her solve this.

She knew that 5 and 2 are equal to 5.

So 5 subtract 2 must be equal to 3.

So well done, whichever way you work that out.

So over to you then.

Task B part 1 is to find the missing numbers to complete the equations.

So you can see we've got some missing equations, we've got some partial number lines with missing parts, and we've also got some bar models with missing parts that you might need to use a few different bits of your knowledge to help you solve.

Then, part 2, you have got some word problems to have a go at, so you might want to use something to help you to represent them.

We've used bar models and 10 frames in this lesson.

So if you have those to hand, they might help you.

Pause this video and have a go at the tasks and come on back to see how you got on.

Welcome back.

So let's see how you got on.

7 subtract 2.

So I can see this as the odd number before 7, which is 5.

5 subtract 2.

3.

3 subtract 2 is 1.

And 9 subtract 2 is 7.

I can see on E that my partial number line is starting with 3.

If I subtract 2, I can use one of the equations in the first part to help me with this one.

3 subtract 2 is 1.

5 subtract 2 is 3.

I can see that my whole in this bar model is 7.

If I subtract 2 from 7, it will give me the odd number before 7, which will be 5.

I could check this by working out 5 plus 2, which I know is the next odd number, which is 7.

So I know that I've got that correct.

And finally, we have our whole, which is 9.

We subtract 2, which gives us the odd number before 9, which is 7.

Well done.

Part 2 then.

Jacob has 7 metres of string.

He cuts 2 metres off and uses it to make a den.

How many metres will he have left? Sam has already given us a clue that 7 metres subtract 2 metres is equal to 7 minus or subtract 2.

She uses her number line and she has landed on the number 5.

So she knows that 2 less than 7 is 5.

5 is the odd number before 7.

So Jacob will have 5 metres left.

Well done if you got that correct.

Sam builds her tower using 5 blocks.

2 of them are yellow.

So how many of those blocks are not yellow? Let's have a look at this using a bar model, 'cause this is really gonna help us to visualise our problem.

We know that there are 5 blocks in total, so that will be our whole.

5 is the whole.

We also know that 2 of them are yellow, so 2 must be a part.

Jacob has suggested that if we subtract 2 yellow blocks from the hole, that will leave the other part.

So he writes the equation 5 subtract 2.

5 subtract 2, we can see this as the odd number before 5, which is 3.

3 is the odd number before 5, so 3 of the blocks are not yellow.

Well done if you've got this correct.

You've done some excellent learning in today's lesson.

So let's have a look at what we have covered.

Adding 2 to an odd number gives the odd number after.

Subtracting 2 from an odd number gives the odd number before.

And when we count backwards in odd numbers, we subtract 2 each time.

The result is 2 less.